True Ancestor

A singular existence amongst the bloodsuckers. Characteristically close to elementals.
They were created by nature, which had no tangible method of self-defense toward humans. Therefore, they are extensions of nature.
“If mankind is to be ruled, let man be the model.” Under this premise, they were created with a mind and body structure similar to humans.
However, there was a birth defect. The True Ancestors bore a flaw, the vampiric impulse.
Each and every True Ancestor is burdened with the desire to drink the blood of the very humans they were meant to rule. And, in order to suppress that impulse, they consume their own willpower.
Those that can change the state of the world merely by thinking are instead forced to use almost all of those “thoughts” to restrain themselves.
But, everything has a limit.
Unable to resolve the problem at its root, the vampiric impulse accumulates, until finally it becomes impossible for them to control with their own power alone.
True Ancestors that have become unable to control their desires fall into an eternal slumber. It could be said that this is the lifespan of those who have no end.
Also, there were those among them that succumbed to their desires and began indiscriminately drinking human blood. Known as Fallen Ancestors, they are powerful to the point that it is said to be completely impossible for humans to oppose them.
Though the True Ancestors possess godlike abilities, the fact that human ideas had no influence on their creation means they are not a type of Divine Spirit. They are an existence desired by the world, but not by humans. Because of this, they have gradually gone into hiding and dwindled in numbers.
Though they have definite form, they can also be considered a kind of Counter Force. …If you want to know what a Counter Force is, please refer to Kara no Kyoukai.

Tsukihime Data Collection: Tsukihime Dictionary
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A type of vampire, but really they are closer to being spirits. Of the available characters Arcueid is a True Ancestor. True Ancestors serve as a defense mechanism for nature, since nature possesses no natural defense mechanism capable of stopping the human race. The True Ancestors have a fatal flaw in that they succumb to vampiric blood sucking impulses, and True Ancestors who fail to resist the urge to suck blood are labeled as Fallen True Ancestors, and hunted by Arcueid. Also, a human who has their blood sucked by a True Ancestor becomes a Dead Apostle.

MB Official Strategy Guide: Melty Blood Glossary
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A singular existence amongst the bloodsuckers. Characteristically close to elementals.
They were created by the planet, which had no tangible method of self-defense against humans. Because of this, it could be said that they are nature’s sense of touch. “If mankind is to be ruled, let man be the model.” Under this premise, they were created with a mind and body structure similar to humans. However, there was a birth defect. The True Ancestors bore a flaw, the vampiric impulse. Probably, it’s because the original that was used as a reference had contained that flaw as well.
Each and every True Ancestor is burdened with the desire to drink the blood of the very humans they were meant to rule. And, in order to suppress that impulse, they consume their own willpower. Those that can change the state of the world merely be thinking are instead forced to use almost all of those “thoughts” to restrain themselves.
But, everything has a limit. Unable to resolve the problem at its root, the vampiric impulse accumulates, until finally it becomes impossible for them to control with their power alone. True Ancestors that have become unable to control their desires fall into an eternal slumber. It could be said that this is the lifespan of those who have no end. Also, there were those among them that succumbed to their desires and began indiscriminately drinking human blood. Known as Fallen Ancestors, they are powerful to the point that it is said to be completely impossible for humans to oppose them.
Their creation was not influenced by human ideas, so they are not a type of Divine Spirit. They are an existence desired by the world, but not by humans. Because of this, they have gradually gone into hiding and dwindled in numbers. Though they have definite form, they can also be considered a kind of Counter Force.
…If you want to know what a Counter Force is, please refer to Kara no Kyoukai.

Tsukihime Dokuhon Plus Period: Tsukihime Dictionary Revised
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A singular existence amongst the bloodsuckers. Characteristically close to elementals.
They were created by the planet, which had no tangible method of self-defense against humans. Because of this, it could be said that they are nature’s sense of touch. However, there was a birth defect. The True Ancestors bore a flaw, the vampiric impulse.
Each and every True Ancestor is burdened with the desire to drink the blood of the very humans they were meant to rule. And, in order to suppress that impulse, they consume their own willpower. Those that can change the state of the world merely be thinking are instead forced to use almost all of those “thoughts” to restrain themselves.
But, everything has a limit. Unable to resolve the problem at its root, the vampiric impulse accumulates, until finally it becomes impossible for them to control with their power alone. True Ancestors that have become unable to control their desires fall into an eternal slumber. It could be said that this is the lifespan of those who have no end.
Year by year their numbers dwindled, until by the time Arcueid was born in the 12th Century, only a hundred individuals remained.
Also, there were those among them that succumbed to their desires and began indiscriminately drinking human blood. Known as Fallen Ancestors (Demon Lords), they are powerful to the point that it is said to be completely impossible for humans to oppose them.

MB Act Cadenza PS2 Manual: Tsukihime Dictionary
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Vampires from birth. For lack of a direct recourse to guard against mankind, the planet created the True Ancestors as its defense. True Ancestors essentially serve as nature’s sense of touch. An unique existence even among blood-sucking species. Can also be thought of as spirits with a physical body.

MB Back Alley Alliance Nightmare: Encyclopedia of Rojiura Nightmare
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The vampires of the beginning.
One of the races of fairy called Elementals which were made independent as the planet’s own sense of touch.
They are a completely different species from the Dead Apostles who were formerly humans, and beings close to limitless immortality, not affected by any religious rite of purification, nor by sunlight.
Receiving back-up from the planet the limits of their activity could be said to be the limits of the natural world itself, and if one thought of the Earth as an individual life form they would be something like leukocytes, equivalent to the main cause of the extermination of humans who prey on nature.
Just as humans perceive the vampires who prey upon themselves as “evil,” for the True Ancestors, the humans who plunder resources while receiving the favor of the planet are “evil”…… That’s how things are.

Tsukihime Material I: Tsukihime Work Glossary
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Those treated as the “original bloodsuckers” in the Tsukihime world.
They are the cause of the vampires who run rampant among the public, even if the True Ancestors themselves are a far cry from the common perception people have surrounding vampires.
They are few in number and exceedingly close to immortal.
Even if they’re exposed to sunlight, it would only ever give them slight anemia. Additionally, they aren’t affected by the cleansing rites employed by any religions either.
True Ancestors are not individuals independent of the natural world like humans are, but an older species still one with nature.
They’re often misunderstood as being undying and eternally youthful because they are the planet’s sense of touch. But the important point is that their time-scale is different from that of humans.
Their lifespan is naturally immense; its limits, so to speak, are only those of nature itself. True Ancestors and fairies are something akin to the planet’s white blood cells. So they possess abilities sufficient to exterminate any of the various factors which would do harm to the planet.
However, at the time of their birth, a singular error occurred within them.
Probably something due to the influence of that after which they were modeled.
They turned out to possess the desire—the primordial, survival-oriented desire—to ingest the blood of intelligent lifeforms.
Moreover, because they were incarnated as protectors, their objectivity was diluted. They gained autonomy, as one of the many species living on the planet. Basically, they came in possession of a sense of values closer to that of humans.

As they have ceased to be free of self-interest—such as noncorporeal elementals ought to be—they have lost sight of their role as protectors, to the point that among them, some have even become like humans, and gained independence from the natural world.
The True Ancestors have no limits.
As a result of being provided back-up from the planet, if the need should arise, they can strengthen their abilities until that need is met. (However, the amount and speed that each True Ancestor can increase it by differs per individual)
In addition, the power of their will is enough to take actual form, meaning that the thoughts of the True Ancestor becomes a weapon on its own, influencing even the world.
Fantasy Materialization—also known as Marble Phantasm—the reformulation of the world through probabilistic fluctuations.
However, they cannot directly interfere with individuals that have become independent from the world, such as humans or animals. By distancing themselves from nature, humans have grown weak, but at same time, won’t perish even if nature itself does, and in doing so, have obtained absolute freedom. At the end of the day, Marble Phantasm can only freely exert change unto the environment and the situation.
As a slight digression, if the ridiculous situation of a castle appearing in the middle of a city at night was to occur, this is thought to be because the vampire (True Ancestor) suzerain of it willed it into creation.

As a species, the True Ancestors are practically gods, but they do still have a flaw.
Though True Ancestors, they are still bloodsuckers. It is the very act of sucking blood itself which serves as their silver stake to the heart.
Though they are the cause that created the vampires (Dead Apostles) on Earth, True Ancestors themselves have zero need to consume blood for survival. The energy they need for that they can get through the ingestion of calories.
That said, they cannot go against their instinct as a species (to ingest and partake in the information of intelligent life = bloodsucking), which ultimately results in them sucking the blood of humans.
They execute humans in order to bring harmony to nature—though in actuality, more than anything else, they need them in order to fulfill their own desires.
This contradiction causes the minds of these proud beings to collapse in on themselves. The more blood these proud elementals suck, the more they degenerate into beasts, craving pleasure the same as any human would.

This degeneration is rightly called “falling to evil.”
True Ancestors which have this happen to them forget the consciousness they have birthed for themselves and become powerful vampires who begin corrupting the world.
As they do not have lifespans, “to lose sight of their values” is the same as their “death of self.”
In order to prevent this death of consciousness, True Ancestors use a large portion of their abilities to inhibit their vampiric urges.
The longer they withstand their desire to suck blood, the larger it grows, and yet, they keep suppressing it in an unending battle of perseverance. By slamming the tremendous power of their will up against their own mind, they can control their desire to drink human blood.
Invariably, as they hold back on sucking blood more and more, the time eventually comes when they realize that they cannot suppress their vampiric urges any longer, at which point they willingly enter into an eternal sleep. This is the activity threshold for those with an endless lifespan—one could perhaps argue it is what humans would actually call their lifespan.

Katatuki Kouhon: World & Tsukihime Character Setting